Strain insulator



July 1, 1958 T. l. MosELl-:Y ETAL 2,841,637.

STRAIN INSULTOR Filed June 29, 1956 JNVENTOR. Tomlinson l Mose/ey 8v By ROD ff SfU/'I nited States STRAIN INSULATOR Application June 29, 1956, Serial No. 594,792

1 Claim. (Cl. 174-163) This invention relates to a strain insulator for mechanically connecting two tension members having different electrical potentials.

A surface ship carrying radio equipment requires an outside antenna which generally comprises a length of electrically insulated wire supported independently above the deck. The antenna wire often is diicult to mount separately on certain types of ships, particularly sailing craft, without creating a problem of interference with the boom and sail-hoisting gear of the ship. A guy wire, mast-supporting cable or similar tension member is suitable electrically for use as an antenna and would overcome the problems of separate antennas if such a tension member could be eiciently electrically insulated without impairing its load-bearing function. Moreover, the problem of providing serviceable outside insulators for seagoing ships has been complicated by salt-water spray which seriously impairs proper functioning of the insulators. Our invention concerns an improved strain insulator for this general purpose and which overcomes the difficulties of insulator breakdown which results from constant exposure to salt-water spray.

An object of our invention is the provision of a compact strain insulator that is capable of withstanding high tensile loads. Another object is the provision of a strain insulator assembly in which the components having different electrical potentials and minimum air space between them are completely enclosed and sealed so that the possibility of leakage between these components as a result of dust, water and other foreign matter is minimized. Still another object is the provision of a strain insulator in which undesirable capacitance is substantially eliminated. A further object is the provision of a strain insulator which will continue to support a tension load in the event of mechanical failure of the insulating material. A more specific object is the provision of a strain y insulator which can be mounted on the end of a cable without necessitating back looping of the cable. A further object is the provision of a rugged, foolproof strain insulator that has a minimum protrusion.

These and other objects of our invention will become apparent from the following description of a preferred embodiment thereof, reference being had to the accompanying drawing comprising a longitudinal section through the insulator assembly.

A preferred embodiment of our invention is shown in the drawing as a generally cylindrical strain insulator 10 symmetrically arranged about a longitudinal axis A and connected at opposite ends to tension members 12 and 13, respectively, which extend outwardly from the insulator along the axis A. By way of example, member 12 may be a link of a turnbuckle that is anchored to the deck of a sail ship and member 13 may comprise a metallic guy wire or cable which extends to the top of the mast. In such an application of our strain insulator, the guy wire is mechanically connected to the mast through another and substantially identical strain insulator so that the length of guy wire between the insulators is elecatent Office g 2,841,633 Patented JulyL 1, 1958 ik trically isolated from the ship structure and as such is suitable for use as an antenna for radio equipment.

Insulator 10 comprises an outer tubular element shown as a cup-shaped, metallic sleeve 15, preferably made of Monel metal, having a cylindrical side wall 16, an end wall 17, and an open end 18 formed with internal threads 19 adjacent to the mouth of the opening. Tension member 12 is mechanically connected to sleeve end wall 17 by suitable means such as a projection 20, which is integral with and extends outwardly from the end wall and which has an aperture 21 by means of which member 12 is secured to the projection. Tension member 13 extends through the open end of the sleeve radially spaced from side Wall 16 and with the inner end 22 of member 13 axially spaced from end wall 17 when the insulator is under load.

In order to adapt the end 22 of member 13 for transmitting tension forces to sleeve 15, an enlarged sleevelike element 24 having a diameter greater than member 13 is secured as by swaging near the end 22 of the member. The end face 25 of element 24, remote from end 22 of member 13, is curved as shown and denes an outwardly extending shoulder on member 13. A frustoconically shaped bushing or inner compression ring 27 disposed coaxially of member 13 ahead of element 24 is formed to seat on shoulder 25 and has a load-bearing face 27a on the side toward the open end of sleeve 15. Element 24 and ring 27 together comprise an abutment on member 13 for transmitting mechanical forces from member 13 to sleeve 15. An electrical insulating ring 28, preferably made of a laminated plastic material such as a melamine reinforced with glass iiber, ts closely haround tension member 13 and engages the inner surface of sleeve 15 for radially supporting the member within the sleeve. Ring 23 has a at face 28a engageable with face 27a of ring 27. The axial forces of member 13 are applied to sleeve 15 through an outer compression ring 30 which preferably threads into the open end of the sleeve and extends in fromv sleeve wall for a limited distance. Ring 30 has an inside diameter substantially greater than the diameter of member 13 and has an inner load-bearing face 30a which engages the adjacent face 28]; of insulating ring 2S. Ring 30 essentially comprises a removable end flange on sleeve 15 and transmits tension forces from sleeve 15 to member 13 through insulating ring 28 and inner compression ring 27. When the strain insulator is fully assembled, ring 30 is axially spaced from the open end of the sleeve and is secured to the sleeve by a plurality of set screws 31. It will be noted that mechanical forces which load the members 12 and 13 in tension are applied in opposite directions against insulating ring 28 so that the latter is stressed mainly in compression. Since electrical insulators generally have maximum strength when stressed in compression, our strain insulator is capable of withstanding tension loads of high magnitude in the order of 15,060 pounds or more without encountering mechanical failure of the insulating material.

insulating ring 28 tits snugly between tension member 13 and the inner surface of sleeve 15 and effectively electrically insulates these parts from each other and likewise insulates the inner compression ring 27 from outer compression ring 30. In order to reduce electrical leakage between ring 27 and sleeve 15, the surface between the outer edge of ring face 27a and sleeve 15 is lengthened by means of an annular rib 32 formed on the face 28a of insulating ring 2S. Rib 32 projects over the adjacent outer marginal edge of compression ring 27 and the inner surface 33 of the rib is spaced outwardly from ring 27. With this arrangement, electrical leakage between proximate parts of ring 27 and sleeve 15 is less likely to occur since the surface of the rib is sufficiently long substantially to prevent such leakage. The opposite or upper face 28!) of the insulating ring is formed with a similar axially projecting annular rib 37 having a smaller diameter than rib 32. Rib 37 extends between compression ring 30 and member 13 and insulates these parts from each other. Insulating ring 37 preferably is counterbored as indicated at 38 effectively to increase the length of the leakage path around rib 37 from ring 30 to the point of contact of the insulating ring with member 13. It will be noted that the inner surface 48 of ring 3b curves outwardly from its junction with rib 37 to further increase the radial spacing between adjacent portions of member 13 and ring 38 and to minimize undesirable capacitance between the parts.

In order to insure that the coupling between tension members 12 and 13 is maintained in the event of a mechanical failure of insulating ring 28, the maximum diameter of face 27a of inner ring face 27 is substantially greater than the minimum diameter of face 30a of outer ring 30, and accordingly these opposed faces of the rings radially overlap each other; that is, portions of ring faces 27a and 30a are axially aligned. The width of radial overlap of ring faces 27a and 30a is sufcient to provide adequate load-bearing engagement between the respective compression rings if insulating ring 28 should fail and continued mechanical coupling of the tension members is assured.,

In order to cover the open end of sleeve 15 and to seal the interior of the strain insulator, a bullet-shaped cap 42 made of insulating material, such as nylon, is threaded into the open end of sleeve 15 and tapers from a maximum diameter at the sleeve to a minimum diameter remote from the sleeve for snug engagement with member 13. A sealing compound 43 seals the outer end of cap 42 to member 13. The exterior of cap 42 preferably is formed with a series of annular ns 44 for improving the surface insulation of the cap.

The procedure for assembling the strain insulator is' as follows: cap 42, outer compression ring 30, insulating ring 28 and inner compression ring 27, in that order, are slipped over the end 22 of tension member 13, and element 24 thereafter is swaged on the end of the tension member. Sleeve 15 is telescoped over the end of mem ber 13 and the compression and insulating rings 27 and 28, respectively; outer ring 30 is threaded into the open end 18 of the sleeve to the position shown in the drawing, and set screws 31 are tightened to lock ring 30 to the sleeve. Cap 42 then is threaded on the end of the sleeve and against outer compression ring 38, and sealing compound 43 is placed around the junction of cover 42 and member 13 to complete the assembly. Tension member 12 is connected to projection 20 on sleeve end wall 17 and tension is appliedthrough the insulator to tension member 13. The other end, not shown, of member 13 is secured in the same manner to another and substantially identical strain insulator which is anchored to a rigid structure. A suitable electrical connection between member 13 and the radio equipment is made.

Modication of and changes to the above descirbed preferred embodiment of our invention may occur to those skilled in the art without departing from the precepts of the invention. Accordingly, the scope of our invention is defined by the appended claim.

We claim: Y

A strain insulator for mechanically coupling two tension members, comprising a cup-shaped sleeve having a longitudinal axis and having one end closed and the other end open, means for connecting one tension member to the closed end of said sleeve, the other member extending into the open end of said sleeve and being spaced from the sleeve, a rst compression ring within and spaced from said sleeve and positively engaging said other member for transmitting an axial force from said other member toward the open end of said sleeve, a second compression ring spaced from said other member and positively engaging said sleeve for transmiting an axial force from said sleeve in opposition to said rst-named force, said compression rings having opposed radially overlapping load-bearing faces, an electrical insulating ring disposed between and in engagement with said faces of the compression rings, said insulating ring having annulalribs projecting axially from opposite ends thereof, one rib being radially spaced from and overlying the load-bearing face of said rst compression ring, the other rib being radially spaced from said other tension member and overlying the load-bearing face of said second compression member, and an insulating cap connected to and extending axially out from the open end of said sleeve, said cap converging into sealed engagement with said other tension member for sealing the interior of said sleeve.

References Cited in the tile of this patent UNITED STATES PATENTS 805,788 Foster Nov. 28, 1905 896,934 Nikonow Aug. 25, 1908 FORElGN PATENTS 239,652 Switzerland Feb. 18, 1946 

